1. Field of Art
The present invention generally relates to soil measurement and testing, and more specifically, automated measurement of soil properties.
2. Description of the Related Art
Nutrient levels in soil have significant spatial and temporal variations. Accordingly, there has been significant effort placed into development of local nutrient management schemes, often referred to as “precision agriculture,” addressing nutrient level variation. Local nutrient management increases agricultural efficiency while reducing its environmental impact by allowing growers to locally apply nutrients where needed. Increases in nutrient costs and a growing awareness of the environmental consequences of current agriculture practices have made improvements in agricultural efficiency and environmental impact increasingly important.
For example, fertilizer inputs are a large fraction of agricultural input costs and prices of nutrient input have almost doubled in recent years, increasing concern about future price fluctuations among growers. Meanwhile, in addition to long-standing concerns about the effect of fertilizers on water quality, greenhouse gas emissions caused by nitrogen-based fertilizers have become an increasing concern. For example, it is estimated that N2O emissions caused by fertilizer volatilization are responsible for 5-10% of the forcing for global warming. Thus the ability to optimize the use of fertilizer inputs, and nitrogen-based fertilizers in particular, is increasingly recognized as a vital component of environmental sustainability. As a result of these factors, there is a rapidly growing interest in more efficient nutrient management.
Local measurement of soil nutrient levels is a significant component of local nutrient management scheme. However, conventional methods for locally measuring soil nutrient levels have limited the effectiveness of existing local nutrient management schemes. Conventionally, capturing a number of samples/acre at the appropriate time to make effective decisions is often prohibitively time consuming and expensive. For example, lettuce growers in certain area typically plant several crop cycles each year, and have a five day window between harvesting and planting the next crop. Logistically, this results in a very small time window, 1-2 days, in which to sample the field and apply fertilizer. This short time frame prevents use of standard laboratory-based soil testing, which often takes 1-2 weeks to provide a result. Consequently, growers typically make decisions on fertilizer application based on historical analysis, instead of on current soil conditions.
As another example, in-season nitrogen management in corn-growing regions is often difficult because of the slow turnaround time of laboratory-based soil testing. Extending the time when corn growers are able to measure soil nitrogen levels would allow corn growers to test fields before their last application of fertilizer. This enables corn growers to test fields later in the growing season and implement nitrogen management practices. Further, allowing growers to promptly retest fields, such as retesting after a rain, allows growers to adopt more efficient nitrogen management practices. Additionally, laboratory-based soil measurement costs scale directly with the number of samples, making it prohibitively expensive to sample at high grid densities. Thus, the development of a fast, simple, and inexpensive soil would expand the benefits of precision agriculture.
Nitrate-nitrogen is one of most important nutrients for a variety of crops, but it is particularly mobile in the soil, making it subject to large spatial variations. Additionally, mapping soil nitrate levels using standard laboratory-based tests is relatively slow and expensive. Accordingly, there have thus been numerous efforts to develop fast soil nitrate detection tools. Technologies used have ranged from mid-infrared (mid-IR) spectroscopy to ion-selective electrodes. However, the use of each currently developed method has suffered from some combination of expense, low accuracy, stringent calibration requirements or difficulty of use.
There have been several recent efforts to perform fast, “on-the-go” measurements of soil nitrate-nitrogen using ion-selective electrodes. While these ion-selective systems have shown the feasibility of making rapid measurements on soil-extractant mixtures, the fragility of the ion-selective membrane itself has caused significant problems with the robustness and reproducibility of soil measurements. Ion-selective systems also require frequent calibration, making them unappealing for routine field use. Nitrate “strip tests”, commonly available from scientific supply stores or from manufacturers, or hand-held spectrometers have also been used. However, nitrate strip tests typically suffer from poor accuracy compared to standard laboratory-based tests and require extensive sample preparation, including consumable reagents. For example, the standard preparation time for nitrate strip tests typically approaches 30 minutes, includes numerous preparation steps and requires precise timing of the reaction steps.
Accordingly, a rapid and economical system for soil analysis could provide more accurate and timely nutrient management recommendations which improve agricultural efficiency.